Electric switch for controlling a flashing-signal lamp



July 10, 1956 A. D. PRICKETT 2,754,391

ELECTRIC SWITCH FOR CONTROLLING A FLASHING-SIGNAL LAMP Filed Nov. 10, 1953 2 Sheets-Sheet 1 Fig.2

Zr2,.u elztop 1 D. Pr (La/ 562 76 July 10, 1956 A. D. PRICKETT ELECTRIC SWITCH FOR CONTROLLING A FLASHING-SIGNAL LAMP 2 Sheets-Sheet 2 Filed Nov. 10, 1953 ln 0 enter if .D, 1 1w; cfici United States Patent ELECTRIC SWITCH FOR CONTROLLING A FLASHING-SIGNAL LAMP Alfred Donald Prickett, Handsworth, Birmingham, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England Application November '10, 1953, Serial No. 391,351

Claims priority, application Great Britain November 29, 1952' 3 Claims. (Cl. 200-113) This invention relates to an electric switch for controlling a flashing signal lamp on a vehicle, the switch being of the kind in which a flexible snap-action member adapted to interrupt "the lamp current intermittently is controlled by a thermally extensible wire carrying the current.

The object of the invention is to provide a switch of the said kind in a simple form.

A switch in accordance with the invention includes a flexible metal contact-carrying strip which is anchored at one end and has its free end secured to the control wire, the said strip having formed therein adjacent to its longitudinal edges a pair of slots, and the part lying between the slots being slightly bowed or strained so that it can operate with a snap action for making and breaking the lamp circuit through associated contacts.

A further feature of the invention comprises the combination with the switch, of an adjustment device carried by the said slotted strip for varying the flashing frequency.

In the accompanying drawings, Figure l is a part sectional side elevation, Figure 2 a front elevation and Figure 3 a rear elevation of a switch embodying the invention. Figure 4 is a diagrammatic view illustrating the action of the switch shown in Figures 1-3, and Figure 5 is a diagrammatic view illustrating the action of a modified form of the switch. Figures 6 and 7 are respectively a front and side elevation illustrating an alternative adjustment means for varying the flashing frequency.

Referring to Figures 1-3, the base a of the switch is formed by a disc of insulating material. To one face of the base is secured a flat post b and from the post extend a pair of flexible metal strips c, d which are insulated from each other at the ends attached to the post, these strips being provided with the circuit-controlling contacts 2, f. The strip 0, which is longer than the other, has formed along a part of its length and adjacent to its longitudinal edges, a pair of slots g, and the marginal parts of the strip alongside these slots are twisted through a right angle to impart relative rigidity to the said edges and also to form a pair of lugs h to be hereinafter referred to. The portion of the strip between the slots which carries the contact e is slightly bowed or strained and is adapted to move relatively to the side parts of the strip with a snap action when a force acting on the free end of the strip is exerted and relaxed. The free end of the adjacent and shorter smaller strip a carries the contact f and its other end is connected to a terminal i on the base.

The free end of the slotted strip 0 is bent through approximately a right angle and to this end is attached one end of a thin control wire j. The other end of the wire is anchored to a support k on the post b above mentioned. Also the wire is connected by a thin metal strip m to another terminal n on the base, the opposite end being connected by a strip p to the strip 0. The wire is anchored to the parts 0, k by glass beads q.

When the wire is cold its tension is such that the strained part of the strip 0 presses the two contacts e, 1 together. When the wire is heated by a current passing 2,754,391 Patented July 10-, 1956 along it, the tension is relaxed and the said part of the strip can then snap to its other position for separating the contacts.

If desired there may be formed on or secured to the above mentioned post b an extension r the free end of which abuts against the rear side of the strained part of the strip c, when the wire is cold, thus ensuring positive deflection of the said part for holding the contacts together.

For adjusting the frequency of the signal flashes, there is supported by the lugs h above mentioned, a spindle s on which is mounted a cam-shaped abutment t adapted to bear against the strip d and to deflect it vto the desired position, the extent of deflection being varied by rotatably adjusting the abutment. In the example shown in the drawing, the strip a has formed in it a slot u, the contact 1 being provided on the part of the strip at one side of the slot and the cam being arranged to act on the part at the opposite side of the slot as shown in Figure 2.

An alternative means for adjusting the flashing frequency is shown in Figures 6 and 7. In this the lugs h of the slotted strip c are interconnected by a screw t The eflect of the screw is to impose a variable strain on the lugs and so vary the rate of action of the part of the strip lying between the slots g.

It will be understood that the switch above described is used to control the flow of current to the bulb of a signalling lamp, the current being under the control of a manually operable switch. When it is required to bring the lamp into action for giving the desired flashing signals (which in one example are used for giving warning of an intended change of direction of the vehicle) the manually operable switch is closed. Current then flowing through the Wire above mentioned heats the wire and causes it to extend sufliciently to relax its normal pull on the slotted strip 0. The strained part then snaps over into the position in which it separates the contacts e, f and so interrupts the current passing along the Wire to the lamp bulb. With the subsequent rapid cooling and shortening of the wire it re-exerts its pull on the slotted strip, thereby causing its strained part to snap over to its other position in which it re-closes the contacts and so again completing the circuit through the lamp bulb. The above described action is then repeated so long as the manually operable switch remains closed. The action of the switch will be readily understood by reference to the diagram at Figure 4. Alternatively the strip d and the contacts 2, 1 may be arranged at the opposite side of the strip c to that shown in Figure 4.

To enable the driver of the vehicle to ascertain that the switch is acting, there may be combined with it an additional strip v as shown in Figure 5, carrying a contact w which co-operates with an additional contact x on the strip 0. These contacts control the circuit of a warning lamp in the vehicle which operates alternatively with the signalling lamp when the switch is acting.

The switch above described may be conveniently enclosed by a protective cover z detachably secured to the base a.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A switch for controlling a flashing signal lamp on a vehicle, comprising in combination a thermally extensible wire through which electric current can flow and which can be heated by the current flow through it, one end of said wire being anchored in a fixed position, a flexible metal strip also having one end anchored in a fixed position and having the other end secured to the other end of said wire, said strip having formed therein adjacent to its longitudinal edges a pair of slots separated by a part of said strip so distorted that it is movable with a snap action in response to thermal extension of said wire, a movable contact carried "by the distorted part of said strip, a complementary contact with Which said movable contact can co-operate, a pair of terminals to which the fixed end of said Wire and said complementary contact are respectively connected, and which form with said wire, strip, and contacts an electric circuit which can be interrupted and re-established by separation and reclosure of said contacts in response to movements of the distorted part of said strip, lugs formed on the longitudin'al edges of said strip and adjustable means carried by said lugs for varying the frequency of separation and reclosure of said contacts.

2. A switch according to claim 1, in which the adjustable means for varying the frequency of separation and re-closure of the contacts comprise in combination a rotatably adjustable cam-shaped abutment for varying the position of the complementary contact, and a spindle on which said abutment is mounted, and which is supa ported by the lugs on the longitudinal edges of the slotted strip.

3. A switch according to claim 1 in which the adjustable means for varying the frequency of separation and re-closure of the contacts comprises a screw sadjustably interconnecting the lugs on the longitudinal edges of the slotted strip.

References Cited in the file of this patent UNITED STATES PATENTS 923,839 Henry June 8, 1909 1,621,020 Matthews Mar. 15,1927 2,225,086 Schramm Dec. 7, 1940 2,388,712 Schmidinger Nov. 13, 1945 2,425,717 Bean Aug. 19,1947 2,672,562 Boddy Mar. 16,1954 2,689,283' Pulvari Sept. 14, 1954 2,700,083 Harmon Jan. 18, 1955 

